The present invention relates to compound semiconductor devices coated with a passivation film which is effective to compound semiconductors including InP and GaAs and manufacturing method thereof.
Previously, an Si.sub.4 N.sub.3 film and an SiO.sub.2 film have been used as passivation films for semiconductor devices. However, especially for compound semiconductors, stress generated at an interface between a passivation film and the semiconductor surface due to the difference of the coefficient of expansion and damage on the semiconductor surface generated in a film deposition process were problems to be solved.
On the other hand, an oxide film as a passivation film is formed on a surface of compound semiconductor by oxidizing the compound semiconductor with aqueous solution of hydrogen peroxide. Refer for example to J. Electrochem. Soc. 118 (1971) pp. 657-658 and Appl. Phys. Lett. 18 (1971) pp. 304-307.
It has been known that an oxidizing agent is prepared by adding Fe.sup.2+, Fe.sup.3+, Cu.sup.+, Cu.sup.2+, Co.sup.2+ or the like to aqueous solution of hydrogen peroxide. Refer for example to "Oxidation and Reduction" (Maruzen, Tokyo, 1978) pp 682-684. This agent has an organic compound as an object for oxidation. The metallic ions included in the oxidizing agent act only as a catalyst, and oxides or hydroxides of metallic ions do not deposit on a specimen. Because physical or chemical adsorption of an oxide or hydroxide of metallic ion takes place on the surface of a compound semiconductor, the deposition of such oxides and hydroxides takes place if a specimen is a compound semiconductor.
However, there were problems to be solved on such a passivation film. First, crystal defects are generated for example due to stress caused by the difference of the coefficient of expansion between the film and the surface of the compound semiconductor, or due to damage of the semiconductor surface formed by diffusion of constituent element atoms into the passivation film and formed in a deposition process of the film. The crystal damages become recombination centers to enhance leakage current. Second, when an oxide film is formed on a surface of compound semiconductor with aqueous solution of hydrogen peroxide, the reaction is very sensitive to impurities contained in the solution and pH so that the reproductivity and stability of the passivation film are bad. Further, an oxide film produced in this way has a relatively large leakage current of 10.sup.-5 to 10.sup.-6 A/cm.sup.2. Further, when the growth of oxide film starts, active state-to-nonactive state transition occurs to dissolve the semiconductor partly. However, the transition occurs with difficulty if only hydrogen peroxide is used, so that it is one of the factors of the instability of the reaction.